1. Field of the Invention
The invention concerns a coil arrangement for contactless guidance of a magnetic element—in particular an endoscopy capsule—in a work space (cooperating space).
2. Description of the Prior Art
The use of endoscopes and catheters is increasingly widely applied in medicine for the diagnosis or the treatment of the inside of a patient. The instruments are introduced into the body via bodily orifices or cuts in the body and can be displaced in a longitudinal direction, directed from the outside, for which a mechanical connection to the instrument is necessary. However, given the forward movement of the instrument into the body, difficulties in the navigation normally occur at curves or branches, in the manner that the operator must direct the instrument in the desired direction, possibly via repeated testing, and a supporting force from the tissue on the instrument is required for the further navigation. This is linked with a large time cost for the operator and with pain for the patient. In the worst case, it is not to be precluded that the guidance in the planned direction is not achieved at all, or that the risk of tissue perforation arises. Furthermore, in the case of endoscopy it can be of interest to rotate the endoscopy head equipped with a camera in specific directions, for example in order to completely view the mucous membrane in a segment of the gastrointestinal tract. With current catheter endoscopes this is only conditionally possible because the catheter tip has only limited mobility. Moreover, typical catheter endoscopes have the disadvantage that remotely situated internal organs can only be reached with difficulty, or cannot be reached at all.
The passive endoscopy capsule moved via the natural peristalsis of the gastrointestinal tract does not have the cited disadvantages, but also cannot be navigated, which means that the targeted viewing of specific points inside the gastrointestinal tract is not possible. Therefore, magnetic navigation or guidance systems have been proposed that enable a catheterless or wireless guidance of endoscopy capsules that contain a magnetic dipole moment. A catheterless or wireless guidance is also designated as “contactless” in the following.
DE 103 40 925 B3 and WO 2006/092421 A1 respectively describe a magnetic coil arrangement consisting of 14 individual coils for navigation of an endoscopy capsule, a video capsule or another probe. The capsule is hereby equipped with a magnetic element, for example a permanent magnet or ferromagnet. The magnetic coil arrangement generates magnetic field components Bx, By, Bz along the axes x, y, z of a Cartesian coordinate system, as well as magnetic gradient fields that enable a contactless guidance of the endoscopy capsule.
Use is made of the fact that the magnetic element—i.e. a body with a magnetic dipole moment {right arrow over (m)}—seeks to align parallel to the direction of the magnetic field {right arrow over (B)} consisting of the magnetic field components Bx, By, Bz in the direction of the axes of the Cartesian coordinate system. Since the magnetic element is firmly connected with the endoscopy capsule, the orientation of the capsule can thus be affected. A force {right arrow over (F)}=G·{right arrow over (m)} with a gradient matrix G comprising the gradient fields, triggered by the magnetic gradient fields ∂Bx/∂x etc., additionally acts on the magnetic dipole moment {right arrow over (m)} according to
      F    →    =                              G          _                _            ·              m        →              =                  (                                                                              ∂                                      B                    x                                                                    ∂                  x                                                                                                      ∂                                      B                    x                                                                    ∂                  y                                                                                                      ∂                                      B                    x                                                                    ∂                  z                                                                                                                          ∂                                      B                    y                                                                    ∂                  x                                                                                                      ∂                                      B                    y                                                                    ∂                  y                                                                                                      ∂                                      B                    y                                                                    ∂                  z                                                                                                                          ∂                                      B                    z                                                                    ∂                  x                                                                                                      ∂                                      B                    z                                                                    ∂                  y                                                                                                      ∂                                      B                    z                                                                    ∂                  z                                                                    )            ·                        m          →                .            
The gradient matrix G is symmetrical and trace-free due to the Maxwell equations rot{right arrow over (B)}=0 and div{right arrow over (B)}=0, meaning that with ∂Bx/∂y (=∂By/∂x), ∂Bx/∂z (=∂Bz/∂x), ∂By/∂z (=∂Bz/∂y) and two of the three diagonal elements (for example ∂Bx/∂x and ∂By/∂y) it contains five independent gradient fields.
The magnetic field {right arrow over (B)} and the gradient fields can be set arbitrarily via a targeted activation of the individual coils of the magnetic coil arrangement. It is therefore possible to rotate the magnetic element and thus to position it arbitrarily in a work space A within the magnetic coil arrangement. It is possible to exert a force {right arrow over (F)} on the magnetic element in order to shift it translationally in addition to the rotation. For this eight quasi-static magnetic degrees of freedom are realized, namely the magnetic field components Bx, By, Bz as well as two of the three entries of the diagonal elements (for example ∂Bx/∂x and ∂By/∂y) and three of the secondary diagonal elements (for example ∂Bx/∂y ∂Bz/∂x, ∂Bz/∂y) of the gradient matrix G.
The systems described in DE 103 40 925 B3 and WO 2006/092421 A1 have the disadvantage that, because of the 14 individually activated coils that are required there, they are relatively cost-intensive in their manufacture and installation due to the high number of coils and power amplifiers.